Process for the preparation of urea from carbonic anhydride and synthetic ammonia



- May 22A, 192s. 1,670,341

' L. CASALE PROCESS FOR THE PREPARATION OF UREA FROM CARBONIO ANHYDRIDE AND SYNTHETIC AMMONIA Filed June 11, 1925 0&7 Kif/@Qd )WM/@ f' MM@ y" urea has recently been the Patented May 22,

LUIGI CASALE, 0F ROME, IT

PROCESS FOB THE PREPARATIO Application lcd June 1 ALY; MARIE CASALE SACCHI ADMINISTBATRIX OF SAID LUIGI CASALE, DECEASED. i

N OFUREA FROM CARBONIO ANHYDRIDE AND SYNTHETIC AMMONIA.

This invention relates to urea and to a method for preparing the saine from ammonia and carbon dioxide or their immediate products of reaction.

Such'preparation of subject of considerable study owing to the importance which the product might have in numerous fields of application.

For instance the temperatures at which the system may reach its equilibrium have been well determined, and it was found that the condition begins to take place at about '150 at lower temperatures,

while,

C., the transformation wise be too slow, can rions catalysts.

C., down to 130 which would otherbe accelerated by va- It was ascertained that the percent-age ot urea in the above mentioned equllibrium system increases with the temperature, the formation of urea being accompanied by a considerable absorption of heat, and it was furthermore ascertained that the percentage of urea in the equilibrium is a function of the pressure of the sys In all of the applications,

said method for the pr tem.

so far tried, of

eparation of urea, the

procedure has been more or less as follows: In an autoclave under pressure carbamate of ammonium or carbon dioxide and ammonia in the required proportions are heated,

with or without temperature additions vof catalyst, to a above 130 C., the final being removed from the autoclave a product ter the transformation and the ureaseparated.

Contmuons operation has also been suggested by gradually autoclave at operatlng pressure,

introducing into the carbon di'- oxide and ammonia in quaptities equivalent to the urea contlnuously removed from the apparatus.

` The cost of this latter operation is obviously high, both as regards cost of installation and power required for heating and compression.

I ave now found plying that the expense of supthe necessary thermic energy may be dis ensed with entirely, while the costs of bot tion can power for compression and of installabe considerably reduced by grafting the production of urea on to the production of synthetic ammonia,

that is to say by in- 1, 1925, Serial No. 36,530, and in Italy December 23, 1924.

serting an apparatus for making urea in an installation (preferably a closed circuit one) for the synthesis of ammonia. For example in an apparatus for the production of synthetic ammonia such as is Patents No. 1,478,549 and No. 1,478,550 the gaseous mixture leaving the catalytic tube contains a high percentage of ammonia at a temperature of about 250 C. and under a pressure of about 800 at. If compressed car'- sists in causing the gaseous mlxture obtained described in U. S.

by catalytic synthesis of ammonia while it is A still under the influence of pressure and heat' to react with carbon dioxide gas, the urea being then separated from the reaction products from which the uncombined nitrogenhydro en mixture with or without ammonia is pre erably recirculated in the process.

The accompanying drawing shows schematically and by way of example only, how the process of this invention may be carried into effect.

Referring to the drawing, the nitrogenhydrogen mixture or even nitrogen-hydrogen-ammonia mixture previously compressed, is passed through the tube 1 and `enters tube 2 where it meets a stream of uncombined nitrogen-hydrogen mixture or such mixture containing some ammonia circulating underthe action of a pu'mp 12. The resulting gaseous mixture passes then through a purifier 3 and by-wa of tube 4 enters a catalytic apparatus 5. he reaction product which now contains a hi h percentage of ammonia leaves the catalytic apparatus 5 by way of tube 6 and enters a chamber 7 which may contain 'a catalytic agent for accelerating the formation of urea, as' for' instance alumina, kaolin, silica and the like. Carbon dioxide is passed by way of tube 8 into the chamber 7 and tlus' reacts with the hot ammoniacal gases forming urea. In the lower part of the chamber 7, which may be cooled, the urea condenses to ether with the Water, simultaneously forme to a liquid which can be drawn off through tube 9. while the gases flowing through the cooling apparatus enter a receptacle 11 where the residual water, ammonium carbonate and ammonia are collected.

The uncombined hydrogen-nitrogen mixture or such mixture containing some ammonia leaving receptacle 1l is recirculated by means of pump 12 through tube 2.

It is advisable to use the carbon dioxide in quantity less than that established in the above mentioned equation of equilibrium, because in this way the gases are very easily and surely restored to the conditions required for proper operation of the apparatus for catalysis.

Claims- 1. The process of preparing urea which comprises reacting nitrogen and hydrogen together under conditions of heat and pressure to form a gaseous mixture containing ammonia, said mixture being at the elevated temperature and pressure of the ammoniaforming reaction and mixing carbon dioxide gas with said gaseous mixture Without substantial diminution of the temperature and pressure thereof to form urea.

2. The process of preparing urea which comprises reacting nitrogen and hydrogen together under conditions of heat and pressure to form a gaseous mixture containing ammonia, said mixture being at the elevated temperature and pressure of the ammoniaforming reaction, approximately 15G-250 C. and 800 atmospheres pressure, and mixing carbon dioxide gas with said gaseous mixture without substantial diminution of the temperature and pressure thereof to form urea.

In testimony whereof I have hereunto signed my name.

LUIGI CASALE. 

